The prior art reclosers included oil filled tanks having the operating mechanisms immersed in oil and were generally self-contained, taking operating energy directly from the system. They included controls that signaled a low-energy solenoid to initiate tripping operation. Reclosing and trip-spring energy was provided by a closing solenoid. There was dual timing of both phase-trip and ground-trip operations provided by proper setting of timing-sequence selectors. Each of these recloser operations was controlled by mechanical means, except for the over-current sensing and trip timing which was controlled by an electronic control.
Arc interruption took place within three sealed, vacuum interrupters. Oil was used in such reclosers for electrical insulation, but was not involved in arc interruption. The oil was also used in the counting mechanism which determined how many times the recloser should cycle before permanent shutdown.
The moving contacts in the vacuum interrupters were pulled open by release of the opening spring. The low-energy tripper, which is operated by the electronic control system, releases the opening spring when current above the minimum trip level, or a ground (earth) fault, is sensed.
The ground (earth) fault tripping feature sensed zero sequence current with sensing current transformers, located inside the recloser. When the zero sequence current exceeds the selected minimum ground-trip level and remains above that level through the selected timing period, the control operates the low-energy tripper to release the contact opening spring.
Closing energy, as well as energy to charge the opening spring, is supplied by a closing solenoid momentarily connected phase-to-phase through a contactor.
In these previous devices the oil filled tank, that was provided as an insulating medium, was sensitive to fire and explosions.